When a projector is disposed and mounted, it is very difficult to make the projector to be perpendicular to a projection curtain and face right to a center point of the projection curtain. At this moment, diffusion of light projected from the side, near the projection curtain, of the projector is smaller than diffusion of light projected from the side, far away from the projection curtain, of the projector. As a result, widths of two sides of an image obtained through projection are different, and consequently a rectangular (square) image becomes trapezoidal. In order to solve trapezoidal image distortion, usually trapezoidal distortion correction is used. Trapezoidal distortion correction refers to shape adjustment and compensation performed by an electronic device on an image before projection through a difference algorithm. However, actual image quality is inevitably reduced.
For applications which do not have high requirements on image accuracy, digital trapezoidal distortion correction can very well solve trapezoidal image distortion, and the practicability is very strong. However, since some lines and character edges of an image become blurred and unsmooth and the definition is poor after the image is subjected to digital trapezoidal distortion correction, it is not suitable for applications which have high requirements on image accuracy, such as CAD drawing display. However, image distortion in a vertical direction caused during projection at an inclined angle can be corrected.
Trapezoidal distortion correction includes vertical trapezoidal distortion correction and horizontal trapezoidal distortion correction. In the related art, angles which can be corrected are limited in an automatic vertical trapezoidal distortion correction technology, a correction range is generally 0°-45°, projectors in the market usually reserve 5° and an actual range is 0°-40°. Since whether a projection plane is a wall or a ceiling cannot be recognized when an included angle between a projector and a horizontal plane exceeds 45° in the automatic vertical trapezoidal distortion correction technology in the related art, if the included angle between the projector and the horizontal angle exceeds 45°, the projection plane is a wall. However, if, at this moment, the projector has already considered that the projection plane is a ceiling, consequently the projector will perform trapezoidal distortion correction as a situation that the included angle is less than 45° when projecting to the ceiling, but the angle of projection to the wall is greater than 45° at this moment. Therefore, automatic vertical trapezoidal distortion correction in the related art cannot realize accurate trapezoidal distortion correction.
For horizontal trapezoidal distortion correction, only partial manufacturers launch manual horizontal trapezoidal distortion correction functions, principle of which are consistent with that of vertical trapezoidal distortion correction. However, automatic horizontal trapezoidal distortion correction functions are not realized, that is, an angle between a projector on a horizontal plane and a wall surface cannot be known.